esp8266/modules/onewire: Change onewire.read() to onewire.readinto().

This allows 1-wire drivers (eg DS18X20) to perform in-place operations and
hence do less memory allocations.

esp8266/modules/ds18x20.py

@@ -8,6 +8,7 @@ _WR_SCRATCH = const(0x4e)
 class DS18X20:
     def __init__(self, onewire):
         self.ow = onewire
+        self.buf = bytearray(9)
 
     def scan(self):
         return [rom for rom in self.ow.scan() if rom[0] == 0x28]
@@ -21,10 +22,10 @@ class DS18X20:
         self.ow.reset(True)
         self.ow.select_rom(rom)
         self.ow.writebyte(_RD_SCRATCH)
-        buf = self.ow.read(9)
-        if self.ow.crc8(buf):
+        self.ow.readinto(self.buf)
+        if self.ow.crc8(self.buf):
             raise Exception('CRC error')
-        return buf
+        return self.buf
 
     def write_scratch(self, rom, buf):
         self.ow.reset(True)

esp8266/modules/onewire.py

@@ -27,11 +27,9 @@ class OneWire:
     def readbyte(self):
         return _ow.readbyte(self.pin)
 
-    def read(self, count):
-        buf = bytearray(count)
-        for i in range(count):
+    def readinto(self, buf):
+        for i in range(len(buf)):
             buf[i] = _ow.readbyte(self.pin)
-        return buf
 
     def writebit(self, value):
         return _ow.writebit(self.pin, value)